Radio-frequency identification (RFID) is a generic term for technologies that use radio waves to automatically identify objects. There are several conventional methods of identifying objects using RFID, the most common of which is to store a serial number and other information that identifies a product on a microchip that is attached to an antenna. The chip and the antenna together define an RFID transponder circuit that is referred to as an RFID tag or RFID label. The tag is very thin and flexible and can include an etched antenna and a miniature chip with a memory for storage of data. The antenna enables a remote reader that has a transceiver to communicate with the chip, and enables the chip to transmit identification information back to the reader when actuated to do so by the reader. The reader converts the radio waves returned from the RFID tag into a form that can then be utilized by a computer.
RFID tags are classified into three different types: active, semi-active, and passive. Active and semi-active tags include a battery to power the microchip. While passive tags are remotely-powered, active tags broadcast their information. Passive tags are the most frequently used since they have a low cost of production and are easily used. Low frequency RFID systems (125-148 kHz) and high frequency RFID systems (13.56 MHz) have short transmission ranges up to 1 meter. Ultra-high frequency (UHF) RFID systems (902-928 MHz) can cover a range up to 10 meters. Microwave frequency RFID systems (2.45 GHz) cover transmission ranges up to 30 meters.
Traditionally, RFID tags have been used for wireless tracking of goods in the retail industry to deal with the problem of inventory management and to act as a theft deterrent. More recently, new applications of RFID technology have been investigated, including the use of RFID tags as sensors to measure parameters such as temperature. When detecting a signal, the sensor produces a measureable output, typically a voltage or current that is related to the signal.